1. Field of the Invention
The invention relates to a double row ball bearing. The invention relates also to a shaft support device including a double row ball bearing.
2. Description of Related Art
As rolling bearings that support a pinion shaft of a differential gear mechanism, tapered roller bearings have conventionally been employed. However, double row ball bearings have recently been employed for the purpose of achieving a reduction of torque (reduction of loss) (see, for example, FIG. 1 in Japanese Patent Application Publication No. 2006-234100 (JP 2006-234100 A)). FIG. 9 is a sectional view illustrating a part of a conventional differential gear mechanism. The differential gear mechanism includes: a case 80; a differential mechanism 81 disposed in the case 80 and including a ring gear 82 and a pinion gear 83; a pinion shaft 84 that rotates together with the pinion gear 83; and a double row ball bearing 90 by which the pinion shaft 84 is rotatably supported.
The double row ball bearing 90 includes: an outer ring 91; an inner ring 92; a plurality of first balls 93 that forms a first ball row; and a plurality of second balls 94 that forms a second ball row. The first balls 93 and the second balls 94 are disposed between the outer ring 91 and the inner ring 92. The first balls 93 and the second balls 94 are in angular contact with raceway grooves of the outer ring 91 and the inner ring 92. The pitch circle diameter of the second ball row formed of the second balls 94 is larger than the pitch circle diameter of the first ball row formed of the first balls 93. A first cage 95 in an annular shape holds the first balls 93 arranged at regular intervals along the circumferential direction. A second cage 96 in an annular shape holds the second balls 94 arranged at regular intervals along the circumferential direction.
The double row ball bearing 90 is disposed near the pinion gear 83, and supports the pinion shaft 84. The ring gear 82 and the pinion gear 83 are lubricated with a lubricant (oil) P1 stored in the case 80, and the double row ball bearing 90 is also lubricated with the lubricant P1. A long dashed double-short dashed line L1 in FIG. 9 represents an oil surface of the lubricant P1.
In the double row ball bearing 90, in order to set the pitch circle diameter of the second ball row formed of the second balls 94 to be larger than the pitch circle diameter of the first ball row formed of the first balls 93, the diameter of one raceway groove of the outer ring 91, on which the second balls 94 roll, is set larger than the diameter of the other raceway groove of the outer ring 91, on which the first balls 93 roll. Thus, as a whole, the inner peripheral surface of the outer ring 91 has such a shape that the diameter thereof is gradually increased toward the pinion gear 83. Hence, when the double row ball bearing 90 rotates, a flow of the lubricant P1 (see an arrow X1 in FIG. 9) is generated between the outer ring 91 and the inner ring 92 (in the internal space of the double row ball bearing 90) in such a manner that the lubricant P1 stored in the case 80 flows from the opposite side (the right side in FIG. 9) of the double row ball bearing 90 from the pinion gear 83, flows through the internal space of the double row ball bearing 90, and is discharged from the pinion gear 83-side (the left side in FIG. 9) of the double row ball bearing 90.
The lubricant P1 stored in the case 80 contains foreign objects, such as machining swarf produced during manufacturing of the case 80, the ring gear 82, and the pinion gear 83, and wear debris produced between the gears 82, 83 during the operation of the differential mechanism 81. Hence, as the volume of the lubricant P1 flowing through the internal space of the double row ball bearing 90 becomes larger, the possibility that the foreign objects contained in the lubricant P1 will be caught between the balls 93, 94 and the raceway grooves of the outer ring 91 and the inner ring 92 increases.
As illustrated in FIG. 9, the lubricant P1 thrown up by the ring gear 82 that is rotating may fall on the second balls 94 of the double row ball bearing 90. In this case as well, the foreign objects contained in the lubricant P1 may be caught between the second balls 94 and the raceway grooves. In addition, rotations of the gears 82, 83 generate a backflow of the lubricant P1 in the case 80. Near the double row ball bearing 90 (the second balls 94), the backflow of the lubricant P1 attempts to proceed toward the second balls 94 (see an arrow X2 in FIG. 9). In this case as well, the foreign objects contained in the lubricant P1 may be caught between the second balls 94 and the raceway grooves.